Method of sealing two substrates with a non-epoxy or epoxy-acrylate sealant using laser radiation

ABSTRACT

A method of joining two panels during the manufacturing of a LCD display employing the ODF (One Drop Fill) assembly technique. Using this method, the liquid crystal is deposited on one of the substrate&#39;s interior to the glue seal. The glue seal is pre-deposited near the peripheral edge of the substrates. The two substrates are then brought in contact with one another. The glue seal must be cured rapidly in order to seal the entire periphery while avoiding contamination between the glue seal, in the liquid state and the liquid crystal. The present invention teaches the use of a non-epoxy glue sealant, which is cured using photoinitiators. Experimental research has discovered the use of photons that are derived from laser beams and the control thereof. This allows for a faster, lower temperature cure.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 09/917,087, filed Jul. 27,2001, now U.S. Pat. No. 7,006,193. The entire disclosure of priorapplication Ser. No. 09/917,087 is herein incorporated by reference.

This is a continuation-in-part of application Ser. No. 09/307,887,entitled “Method of Forming Liquid Display Panels and The Like”, filedMay 10, 1999, now U.S. Pat. No. 6,636,290. The entire disclosure ofprior application U.S. Pat. No. 6,636,290 is herein incorporated byreference.

PARTIAL WAIVER OF COPYRIGHT

All of the material in this patent application is subject to copyrightprotection under the copyright laws of the United States and of othercountries. As of the first effective filing date of the presentapplication, this material is protected as unpublished material.However, permission to copy this material is hereby granted to theextent that the copyright owner has no objection to the facsimilereproduction by anyone of the patent documentation or patent disclosure,as it appears in the United States Patent and Trademark Office patentfile or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to the field of joining two substrateswith a sealant, and more particularly the art of using laser radiationfor curing the sealant during the manufacturing of LCD (Liquid CrystalDisplay) panels.

2. Description of the Related Art

LCD displays are manufactured by joining two substrates to one anotherwith liquid crystal material between the two substrates. Both substratesare typically glass. One method for joining the two substrates to form apanel is related to U.S. Pat. No. 5,263,888 by Ishihara et al in whichan ODF (One Drop Fill) method for assembling liquid crystal flat paneldisplays is described. Using this method, the liquid crystal isdeposited on one of the substrate's interior to the glue seal. The glueseal is pre-deposited near the peripheral edge of the substrates. Thetwo substrates are brought in contact with one another. The glue sealmust be cured rapidly in order to seal the entire periphery.Accordingly, a need exists for a method of curing the glue seal for usein a high quality, high volume but low-cost manufacturing environment.

The strength of the cured sealant holding the two substrates together isalso prime consideration. Since the liquid crystal material is inside ofthe panel prior to cross linking, it is not possible to utilize thestandard thermal baking of the glue seal for curing since thetemperature required for thermal cross linking generally exceeds thetemperature the liquid crystal can tolerate. Accordingly, a need existsfor a non-thermal method for curing the sealant material allowing thesealant method to stay below a temperature that is harmful to the liquidcrystal material.

Furthermore, the thermal process for curing the sealant generally takeson the order of 1 hour or more. During this time, there is a greatchance for intermixing of the non-epoxy glue seal and the liquidcrystal, which leads to eventual poisoning of the liquid crystalresulting in severe defects in the operation of the display panel.Accordingly, a need exists for a fast method of curing the sealant,which does not allow sufficient time for intermixing of the glue sealantin a liquid state and the liquid crystal material.

Another method for curing non-epoxy sealant is to incorporate photoinitiators in the sealant rather than thermal initiators. Lasers havebeen shown to offer both speed and efficiency when photo initiators arepresent in the non-epoxy glue sealant. The use of a laser allows forthis efficient light source to rapidly cure the sealant without anunwanted temperature rise extending into the liquid crystal. There aremany factors when using lasers that must be considered including thelaser frequency, whether the laser is pulsed versus non-pulsed, thepower of the laser, and the exposure time and direction of the laser. Anattempt must be made here to find several commercially availablesolutions that will work and yet provide a cost effective manufacturingsolution. Accordingly, a need exists for the determination of a viableselection of the type of laser and the exact exposure method.

One disadvantage of non-thermal curing methods is that the light sourcemust have a clear light path to the sealant. LCD panels are constructedwith circuit traces that exit the edge of the panel. These circuittraces are used by the display driver to effect the intended image onthe panel. However the traces cause blocking or shadowing of the sealantthat is under the traces. Accordingly the need exists for a method toallow for the light source to be able to reach the sealant that is underthe circuit traces.

SUMMARY OF THE INVENTION

Briefly, according to the present invention, disclosed is a process, andsystem for joining two substrates to form a panel using a laser to curea non-epoxy sealant such as an epoxy-acrylate, epoxy-amine,epoxy-urethane, epoxy-alcohol, epoxy-acid and the like, well know tothose skilled in the art. The distinction here is that none of thecompounds listed here are pure epoxies in terms of organic chemistry. Apulsed laser beam is used to promote the polymerization of the sealantin timely fashion, while not causing a harmful temperature rise to theadjacent glue seal.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

FIG. 1 is a graph of the pull strength versus the UV dosage for a shortpulsed laser and a CW UV (Continuous Wave Ultraviolet) lamp for thepurposes of curing the sealant of a LCD, according to the presentinvention.

FIG. 2 is a graph of the pull strength versus the irradiation for both adifferent UV lamp and laser from that used in FIG. 1, here a pulsed UVlaser for the purposes of curing the sealant, according to the presentinvention.

FIG. 3 illustrates the laser scanning of a panel to cure of thenon-epoxy glue sealant, according to the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

It is important to note, that these embodiments are only examples of themany advantageous uses of the innovative teachings herein. In general,statements made in the specification of the present application do notnecessarily limit any of the various claimed inventions. Moreover, somestatements may apply to some inventive features but not to others. Ingeneral, unless otherwise indicated, singular elements may be in theplural and vice versa with no loss of generality.

DETAILED DESCRIPTION OF THE PROCESS

A method is disclosed to polymerize a non-epoxy glue sealant to rigidlyaffix two substrates to one another by using laser radiation to activatephoto initiators that leads to the cross linking or polymerization ofthe glue seal. Pull strength data is presented of glass samples affixedto one another with non-epoxy glue seals using the mercury UV lamp andtwo different short-pulsed lasers. As further described below, sealingthe periphery of two substrates using lasers to activate the photoinitiators forming a panel already containing the liquid crystal, suchas the ODF technique, offers several advantages compared to that whichresults from using a standard mercury lamp. In another embodiment,thermal initiators are present in the non-epoxy sealant. The thermalinitiators lead to sealant curing when sealing occurs by way ofincreased temperature or baking of the LCD panels.

Experimental Research for Use During the Assembly of LCD Panels

When a UV curable sealant, here limited to non-epoxy sealants such asthose previously described, is exposed to UV (Ultraviolet) radiationphoto initiators are released. These photo initiators interact withchemical portions of the sealant to cause the sealant to cross-link orpolymerize. This is also known as curing. The state of the manufacturingart typically uses UV lamps for irradiation to cause polymerization. Ithas been determined experimentally that a laser, particularly a UV laseris more efficient than UV lamp irradiation. The laser is incident on oneof the UV transparent or near transparent substrates, which is typicallyglass for the optimum efficiency in curing the sealant. The efficiencyis defined here as the pull strength/cross sectional area (CSA) of theglue seal necessary to separate the two substrates. Further defined, theefficiency is the pull strength (the force per unit area of non-epoxyglue sealant) versus the total incident W energy per square cm(fluence).

It has been further determined that pulsed lasers are able to use lesstotal fluence to achieve curing or polymerization compared to UV lampirradiation thereby leading to a faster cure process and a greaterthroughput in manufacturing.

In one embodiment several lasers, an excimer XeF pulsed laser and aQ-Peak high repetition laser are most efficient. Both have pulse widthson the order of 10's of nanoseconds and are more efficient than severaldifferent UV CW (Continuous Wave) lamp sources normally employed foractivating the photo-initiators within the sealant giving rise to asealant cure or polymerization. However, it also possible to use muchshorter pulse width lasers, for example in the femto-second range, sothat the over-all pulse width range can vary from femto-second tocontinuous wave.

Details of the Research

A sealant is applied near the periphery of one substrate to affix thefirst substrate to a second. At least one of the substrates is mostlytransparent to the laser beam radiation. Except in the regions ofmetalization, which are on the underside of the otherwise transparentsubstrate. It is this substrate that the polymerzing light is incidenton in most cases. In the preferred embodiment, the two substrates areaffixed in order to form a liquid crystal display panel. This method isparticularly useful when using the ODF (One Drop Fill) method where itis important to minimize the time in which the sealant, in the uncuredstate and liquid crystal can interact. Given this structure to performresearch several UV sources are investigated.

The lasers have been shown by measurements to be superior in the speedof the polymerization step and the bonding strength compared to severalfocused and unfocused UV lamps which are used as a comparison. In thepresent invention a laser, preferably a pulsed laser, is used to scannear the periphery of one of the two substrates to be affixed to oneanother in the region of the non-epoxy glue seal. The laser light isincident on a transparent or nearly transparent substrate with the laserbeam approximately normal to the plane of the substrate. While the beamcan also enter the substrate at slant angles, that is angles deviatingsomewhat from the normal direction, the reflective losses will begreater and hence the laser less efficient in transferring the light tothe non-epoxy sealant. Never the less the laser can be aimed at an angleoff of normal to the top of the substrate, so as to expose the non-epoxysealant than is under any blocking images. These blocking images includethe circuit traces on the underside of the transparent substrate, whichare used for the pixel selection. When this technique is used care istaken to account for the reflective losses. That is the laser lightimpingement angle and power is adjusted so as to assure the correctamount of irradiation into the non-epoxy sealant independent of how thelight arrived. Unlike an unfocused UV lamp that floods the target thelaser is scanned along the glass targeting the non-epoxy glue seal usingscanning mirrors or robotic arms programmed to follow the desired pathof the glue seal. Typical non-epoxy glue seals require a fluence on theorder of 2-4 J/cm² to cure or cross link sufficiently for cross linkingto be considered complete. Other fluences less than 0.02 J/cm² may alsobe used advantageously in the present invention.

Pull Strength vs UV Dosage for a Lamp and a Q-Peak Laser

FIG. 1 shows experimental data plotted on graph 100 indicating theadvantage of using a pulsed laser to polymerize a non-epoxy glue sealantbetween two small glass samples compared to that of a UV lamp. Theabscissa is labeled UV dosage in J/cm² starting at 0 and ending with2.9. The ordinate is labeled as pull strength of kg/mm² starting at 0.05and ending at 0.275. The pull strength is the force/mm² required toseparate two glass samples. The non-epoxy glue that was used is anepoxy-acrylate glue. The square data points are for the UV lamp whichhad an output of ˜7 mw/cm² at the sample surface. The diamond datapoints are for a Q-Peak™ Nd:YLF frequency tripled laser at a repetitionrate of 10 kHz. It is observed that for all UV dosages the pull strengthof the laser samples is higher then that of the UV lamp.

Pull Strength vs UV Dosage for a Lamp and a Pulsed Excimer Laser

Turning now to FIG. 2 shown is a graph 200 indicating the advantage ofusing a yet another pulsed laser to polymerize a non-epoxy glue sealantcompared to that of an UV lamp. The abscissa is labeled UV Dosage inJ/cm² starting at 0 and ending with 7.0. The ordinate is labeled in pullstrength of kg/mm² starting at 0.075 and ending at 0.4. The pullstrength is the force/mm² required to separate two glass samples. Thenon-epoxy glue that was used is a second epoxy-acrylate. The square datapoints are for the UV lamp source with a high power output of 200mw/cm². The diamond data points are for a Lambda Physik™ XeF pulsedlaser, unfocused, ˜10 Hz, with a fluence of 30 mJ/cm²/pulse. It is againobserved that for all UV dosages the pull strength of the laser samplesare higher that of the UV lamp.

Laser Scanning of Target Substrates

FIG. 3 is an isometric drawing 300 of two substrates that are affixed toone another 302 and 304 with a non-epoxy glue sealant applied near anouter periphery of one of the two substrates. A laser 306 emits a laserbeam 308, which is driven with a power source 310. It is mechanicallycontrolled 312 to scan over the top substrate, which is mostlytransparent to the incident laser light to cure the non-epoxy gluesealant. Robotic means are used to move either the laser or thesubstrate with respect to the laser along the path of the non-epoxysealant. Alternatively Laser scanning is also achieved through the useof scanning mirrors.

Discussion of Photonic Exposure for the Curing Non-Epoxy Sealants

The present invention as would be known to one of ordinary skill in theart could be produced in a several ways. However in one embodiment theinvention is implemented using a particular laser and process whichtaken together are considered a preferred embodiment. The particularprocess and art have been discovered during experimental research.

According to the inventive principles as disclosed in connection withthe preferred embodiment, the invention and the inventive principles arenot limited to the particular kind of laser system but may be used withany similar laser light source, as would be known to one of ordinaryskill in the art.

The invention is not limited to any particular end product such as a LCDdisplay but may be applied to any similar structure for use in alternateproducts, as would be known to one of ordinary skill in the art.

NON-LIMITING EXAMPLES

Although a specific embodiment of the invention has been disclosed, itwill be understood by those having skill in the art that changes can bemade to this specific embodiment without departing from the spirit andscope of the invention. The scope of the invention is not to berestricted, therefore, to the specific embodiment, and it is intendedthat the appended claims cover any and all such applications,modifications, and embodiments within the scope of the presentinvention.

1. A Liquid Crystal Display fabrication apparatus comprising: a LiquidCrystal Display holder adapted to hold a Liquid Crystal Display assemblybeing fabricated, the Liquid Crystal Display assembly comprising: afirst substrate; a non-epoxy glue sealant comprising photoinitiators, afirst side of the non-epoxy glue sealant applied to an outer peripheryof the first substrate, wherein the non-epoxy glue sealant is a materialselected from the group consisting of epoxy-acrylate, epoxy-amine,epoxy-urethane, epoxy-alcohol and epoxy-acid; and a second substrateaffixed to a second side of the non-epoxy glue sealant, the second sideof the non-epoxy glue sealant being opposite the first side of thenon-epoxy glue sealant; and a directable beam laser that produces laserbeam radiation able to be directed relative to the Liquid CrystalDisplay holder so that the non-epoxy glue sealant is cured by directingthe laser beam radiation onto a portion of the first or the secondsubstrate that is at least partially transparent to the laser beamradiation, the laser beam subtending an angle at non-normal incidencewith respect to the first or the second substrate, thereby enabling thelaser beam radiation to pass through the first or the second substratesonto the non-epoxy glue sealant so as to irradiate and polymerize thenon-epoxy glue sealant.
 2. The Liquid Crystal Display fabricationapparatus according to claim 1, wherein the directable laser comprises alaser controlled by a servo to trace out, with the laser beam radiation,a pattern of the non-epoxy glue sealant, the directable laser deliveringnot less than 0.02 J/cm² to the non-epoxy glue sealant.
 3. The LiquidCrystal Display fabrication apparatus according to claim 1, wherein thedirectable laser comprises scanning mirrors to direct the laser beamradiation to deliver not less than 0.02 J/cm² to the non-epoxy gluesealant, the scanning mirrors directing the laser beam radiation totrace out a pattern of the non-epoxy glue sealant.
 4. The Liquid CrystalDisplay fabrication apparatus according to claim 1, wherein the laserbeam radiation provides an Ultraviolet dosage into the non-epoxy gluesealant of not less than 0.02 J/cm².
 5. The Liquid Crystal Displayfabrication apparatus according to claim 1, wherein the Liquid CrystalDisplay assembly comprises a Liquid Crystal Display panel assembledaccording to a One Drop Fill method.
 6. The Liquid Crystal Displayfabrication apparatus according to claim 1, wherein the laser beamradiation comprises laser beam radiation at a wavelength range of200-1500 nm.
 7. The Liquid Crystal Display fabrication apparatusaccording to claim 1, wherein the laser beam radiation comprisescontinuous wave laser beam radiation at a wavelength range of 200-1500nm.
 8. The Liquid Crystal Display fabrication apparatus according toclaim 1, wherein the directable laser comprises a Nd:YLF frequencytripled pulsed laser.
 9. The Liquid Crystal Display fabricationapparatus according to claim 1, wherein the second substrate forms aback side of the Liquid Crystal Display assembly, and wherein thedirectable laser produces laser beam radiation that irradiates thenon-epoxy glue sealant through the second substrate at a pointcontaining no circuit traces.
 10. The Liquid Crystal Display fabricationapparatus according to claim 1, wherein the first substrate comprises acircuit trace that obscures at least part of the non-epoxy glue sealantto light with normal incidence relative to the first substrate, andwherein the laser beam radiation irradiates the at least part of thenon-epoxy glue sealant obscured by the circuit trace.
 11. A LiquidCrystal Display fabrication apparatus comprising: a Liquid CrystalDisplay holder adapted to hold a Liquid Crystal Display assembly, theLiquid Crystal Display assembly comprising: a first substrate; anon-epoxy glue sealant comprising photoinitiators, a first side of thenon-epoxy glue sealant applied to an outer periphery of the firstsubstrate, wherein the non-epoxy glue sealant is a material selectedfrom the group consisting of epoxy-acrylate, epoxy-amine,epoxy-urethane, epoxy-alcohol and epoxy-acid; and a second substrateaffixed to a second side of the non-epoxy glue sealant, the second sideof the non-epoxy glue sealant being opposite the first side of thenon-epoxy glue sealant; a laser that produces laser beam radiation thatirradiates the non-epoxy glue sealant; and a controller for controllingthe laser to scan over the first substrate or the second substrate,wherein the non-epoxy glue sealant attach the first substrate and thesecond substrate with a pull strength of at least 0.15 kg/mm².
 12. TheLiquid Crystal Display fabrication apparatus according to claim 11,wherein the Liquid Crystal Display assembly forms a Liquid CrystalDisplay panel assembled according to a One Drop Fill method.
 13. ALiquid Crystal Display, comprising: a first substrate; a non-epoxy gluesealant comprising photoinitiators, a first side of the non-epoxy gluesealant applied to an outer periphery of the first substrate, whereinthe non-epoxy glue sealant is a material selected from the groupconsisting of epoxy-acrylate, epoxy-amine, epoxy-urethane, epoxy-alcoholand epoxy-acid; a second substrate affixed to a second side of thenon-epoxy glue sealant, the second side of the non-epoxy glue sealantbeing opposite the first side of the non-epoxy glue sealant; and a laserthat produces laser beam radiation that irradiates the non-epoxy gluesealant, wherein the laser beam radiation is directed onto the first orthe second substrate that is at least partially transparent to the laserbeam radiation, the laser beam radiation subtends an angle at non-normalincidence with respect to the first or the second substrate, therebyenabling the laser beam radiation to pass through the first or thesecond substrates onto the non-epoxy glue sealant so as to irradiate andpolymerize the non-epoxy glue sealant, and the laser beam radiationprovides an Ultraviolet dosage of not less than 0.02 J/cm² onto thenon-epoxy glue sealant under any circuit traces within the LCD panel.14. The Liquid Crystal Display according to claim 13, wherein the laserbeam radiation is generated by a Nd:YLF frequency tripled pulsed laser.15. The Liquid Crystal Display according to claim 13, wherein the secondsubstrate forms a back side of the Liquid Crystal Display, and whereinthe laser beam radiation irradiates the non-epoxy glue sealant through asecond side of the second substrate at a point containing no circuittraces, the second side of the second substrate being opposite the sideaffixed to the non-epoxy glue sealant.
 16. The Liquid Crystal Displayaccording to claim 13, wherein the non-epoxy glue sealant attach thefirst substrate and the second substrate with a pull strength of atleast 0.15 kg/mm².
 17. The Liquid Crystal Display according to claim 13,wherein the first substrate comprises a circuit trace that obscures atleast part of the non-epoxy glue sealant to light with normal incidencerelative to the first substrate.
 18. The Liquid Crystal Displayaccording to claim 17, wherein the first substrate and the secondsubstrate form a LCD (Liquid Crystal Display) pane 49 assembledaccording to an ODF (One Drop Fill) method.